Artibeus aztecus, K.Andersen, 1906, K.Andersen, 1906

Hernández-Chávez, Iván, Guevara, Lázaro, Arroyo-Cabrales, Joaquín & León-Paniagua, Livia, 2023, Ecological niche differentiation among Aztec fruit-eating bat subspecies (Chiroptera: Phyllostomidae) in Mesoamerica, Therya 14 (1), pp. 39-47 : 42-44

Discussion

Potential distributions and geographical barriers. The niche models and potential distribution maps seem to support the findings of the habitat preference of the Aztec fruit-eating bat populations reported previously. Mesoamerican highlands, where the models indicate the potential distribution for each subspecies, include a complex assemblage of montane ecosystems containing high biodiversity and endemism ( Parra-Olea et al. 2012; Bryson et al. 2018; Blair et al. 2019). Less-suitable areas, such as the Isthmus of Tehuantepec and the Nicaraguan Depression, may act as current geographic barriers to dispersal, limiting contact between the populations, as proposed previously for the subspecies A. a. aztecus and A.a.minor ( Davis 1969; Peterson et al. 1999).

Isthmus of Tehuantepec has been proposed as a biogeographic barrier associated with allopatric speciation in a broad range of taxa ( Sullivan et al. 2000; León-Paniagua et al. 2007; Castoe et al. 2009; Daza et al. 2010; Rodríguez-Gómez et al. 2013, 2021) and, climatically, has been considered a barrier for dispersal of oak species, and by separating tropical ecosystems from those with more substantial Nearctic influence ( Rodríguez-Correa et al. 2015). The climatic effect of this barrier on the subspecies A. a. aztecus and A. a. minor contrasts with the similar niches found between two haplogroups of the Honduran yellow-shouldered bat Sturnira hondurensis , another Mesoamerican highland bat ( Hernández-Canchola 2018).

On the other hand, the Nicaraguan Depression has been considered a major feature determining genetic and biogeographic patterns ( Gutiérrez-García and Vázquez-Domínguez 2013). The evolutionary impact of this barrier is reflected in genetic differentiation between sister taxa of vertebrates, including birds ( Puebla-Olivares et al. 2008; Arbeláez-Cortés et al. 2010) and snakes ( Castoe et al. 2009). Our findings about the separation between A. a. minor and A. a major are similar to the conclusions of Torres-Morales (2019), who considered Nicaraguan Depression as a significant barrier that limits the distribution of Sturnira hondurensis , separating it from its sister species S. burtonlimi .

Speciation, and species limits. There is a debate about how conserved the niches between closely related lineages are ( Wiens and Graham 2005). Some previous studies have suggested the presence of phylogenetic niche conservatism in phyllostomid bats ( Peterson et al. 1999; Stevens 2006, 2011; Warren et al. 2008), indicating that closely related species share the same climatic preferences. Alternatively, other authors have not found strong support for niche conservatism in phyllostomid bats ( Peixoto et al. 2017), suggesting their niche may have evolved either under strong selection or randomly ( Diniz-Filho et al. 2010).

However, former phylogenetic niche conservatism may promote ecological speciation. It can occur in areas with high geographic and ecological variations. In such regions, any geographic distance also results in environmental distance, promoting niche divergence. The combined topographic variation and ecological distance reduce dispersal and gene flow between adjacent populations ( Gascon et al. 2000; Gehring et al. 2012). Lineages may thus adapt to local niches, leading populations to diverge from the ancestral niche ( Pyron et al. 2015).

Here, we found signals of ecological niche differentiation among the three subspecies of Aztec fruit-eating bat ( Tables 1 and 2 , Figures 2 and 3 ). The three subspecies of A. aztecus present different climatic preferences that may indicate they are evolving independently. Therefore, further studies are necessary to learn about the evolutionary history of A. aztecus and clarify the taxonomic situation of the three subspecies. Certaintly, it is crucial to consider that the outcome and the interpretation of the similarity tests may be sensitive to the definition of the calibration area and environmental background ( Warren et al. 2010), still, they may offer some guidelines to explore speciation mechanisms ( Tocchio et al. 2015) and thus determine the taxonomic status of the species. In this study, we defined it using the movement data of a congeneric species of A. aztecus , so the results must be carefully interpreted. Further details on the dispersal capacity for each subspecies might improve reference area estimation for niche models.

It is essential to clarify the phylogenetic relationships among the subspecies to better understand their biogeographic history ( Martínez-Gordillo et al. 2010). Studies that analyzed the diversification of Artibeus and the subgenus Dermanura , have included a few samples of at least two subspecies, but not A. a. major ( Owen 1987; Hoofer et al. 2008; Redondo et al. 2008; Solari et al. 2009; Baker et al. 2016). Solari et al. (2009) recovered two clades of A. aztecus , represented by samples of A. a. aztecus and A. a. minor, with a genetic divergence of 3.6 % between them, a value that falls in the range necessary for species recognition suggested by Baker and Bradley (2006), so it is crucial to analyze the genetic divergence between the species using a larger number of samples that includes the three subspecies. In addition, morphological analyses that include all subspecies are necessary to assess phenotypic variation and its potential correlation with environmental conditions. A relationship between environmental conditions and morphology has been documented in other Mesoamerican montane species ( Rodríguez-Gómez et al. 2013, 2021; Hernández-Canchola 2018).

In sum, our results offer a first look at the ecological variation of Artibeus aztecus and an additional view on understanding the processes that have shaped the diversification of montane bats in Mesoamerica. Climatic divergence among the three subspecies probably are due to the interaction between former ecological niche conservatism and the emergence of geographic barriers, such as the Isthmus of Tehuantepec and the Nicaraguan Depression that promoted the subsequent ecological differentation.

Figures

Figure 2. Maxent predicted potential distribution for (a) Artibeus a.aztecus, (b) A.a. minor, and (c) A.a.major.

Figure 3. Niche overlap values for Schoener's D and Hellinger's I compared to a null distribution: (a) Artibeus a. aztecus (yellow) vs. A.a. minor (blue), (b) A.a. aztecus vs.A.A. major (red),(c) A.a.minor vs.A.a.major.